1. Field of the Invention
The present invention relates to apparatus, methods and products for the production of hydrocarbons. In another aspect, the present invention relates to methods, apparatus and products for the production of hydrocarbons with sucker rod pumps. In even another aspect, the present invention relates to methods, apparatus and products useful in the operation of a sucker rod pump during the production of hydrocarbons.
2. Description of the Related Art
Hydrocarbons are often produced from wellbores by sucker rod pumps.
These “sucker rod” pumps are reciprocating pumps driven from the surface by pumping units that move a polished rod up and down through a packing gland at a wellhead. The unit may be of the predominant beam type or any other type that reciprocates the polished rod. For example, a beam pumping unit utilizes a walking beam pivotally mounted on a Samson post with one end of the beam being attached to the rod and with the beam being reciprocated by a drive unit. The drive unit consists of a prime mover connected to a reduction unit that drives a crank to reciprocate the walking beam.
The polished rod extends, via a sucker rod string, to a cylinder above, below, or in a portion of an oil producing strata. The sucker rod string is connected to a downhole pump. This downhole pump generally includes a plunger within the cylinder, the plunger including a checkvalve allowing liquids to pass upward through the valve but not downward. This check valve is referred to as a traveling valve. A second check valve is located at the bottom the cylinder that allows liquids to enter the cylinder but not leave the cylinder in the downward direction. The second check valve is referred to as a standing valve. Raising the polished rod therefore lifts the plunger, draws liquids into the cylinder through the standing valve, and lifts the cylinder contents above the plunger up through a tubing string toward the surface. The down stroke of the polished rod lowers the plunger, allowing the contents of the cylinder below the traveling valve to pass through the valve to above the traveling valve.
While sucker rod pumps are relatively simple units, they are generally expensive to provide and maintain.
Repair of seals around the plunger, standing valve, or traveling valve require lifting of the entire down-hole unit by the sucker rod or tubing string to the surface. It is not unusual to have a mile or more of sucker rods or tubing that must be lifted and disassembled by one or two twenty five or thirty foot long sections at a time. This repair is costly in terms of repair labor and parts cost, and in the terms of lost revenue from the well.
Power requirements of the sucker rod pump are also not insignificant, and are greatly effected by the efficiency at which the unit is operating.
Because the marginal additional cost of a larger sucker rod pump is negligible compared to the time value of money realized by producing oil from the well at a faster rate, sucker rod pumping units are typically designed to pump slightly more than the well can produce. Consequently, sucker rod pumps therefore eventually run out of liquids to pump, and draw gas into the cylinders through the standing valves, a condition known as running pumped off.
This term “pumped-off” is used to describe the condition where the fluid level in the well is not sufficient to completely fill the pump barrel on the upstroke. On the next downstroke the plunger will impact the fluid in the incompletely filled barrel and send shock waves through the rod string and other components of the pumping system. This can cause harm to the pumping system such as broken rods or damage to the drive unit or downhole pump.
To minimize running pumped off, sucker rod pumps are generally operated with some type of controller. These controllers are either simple controllers designed not to detect a pump off condition, but rather to avoid an estimated pump off condition, or are more sophisticated pump-off controllers designed to detect when a well pumps off and to shut the well down.
An example of these simple controllers are clock timers that start and stop the pumping unit in response to a set program designed to avoid a pump off condition. For example, if 2 hours of pumping results in a pumped off condition, and it will take 5 hours for sufficient fluid to enter the casing, then the time clock would run the pump for 2 hours (or slightly less to be conservative), and then shut the pump off for 5 hours (or slightly more to be conservative), with 2 hour on/5 hour off cycle continuing until conditions warranted a change. Unfortunately, these simple clock timers are not responsive to changing conditions, such as changes in the reservoir, or the occurrence of abnormal operating conditions. Such a changing condition may occur, with the timer continuing its on/off cycle until human intervention (which may be long after damage to the pump has occurred).
These abnormal conditions of sucker rod pump operation can also be detrimental to the pump, and the well efficiency, and many of these abnormal conditions can be detected by accurate monitoring of the pump operation. For example, a few of the abnormal conditions include, running pumped off, tubing movement, fluid pound, gas interference, inoperative pump, pump hitting up or down, bent barrel, sticking pump, worn plunger or traveling valve, worn standing valve, worn or split barrel, fluid friction, and drag friction. As many of these problems gradually appear and progressively worsen, early detection of these problems can often minimize the cost of maintenance, minimize the cost of inefficient operation, and prevent or minimize the loss of production.
As could be guessed, numerous methods have therefore been proposed to monitor and control sucker rod pump operation.
An example of the more sophisticated pump-off controllers designed to detect when a well pumps off and to shut the well down, include the very common commercially available controllers that monitor work performed, or something that relates to work performed, as a function of polish rod position. This information can be used to determine, for example, if the liquids are pumped off, or if valves are leaking or stuck, and can provide data useful in trouble shooting a wide variety of other problems.
This information is generally presented in the form of a plot (as both are measured at the surface) of load vs. rod string displacement (or position) on the rod string. For a normally operating pump, the shape of this plot (known as a “surface card”), is generally an irregular football shape. The area inside of this rectangle is proportional to the work being performed. Many pump off controllers utilize a plot such as this to determine when the sucker rod pump is pumped off, and then shutdown the pump for a time period when a criteria indicating the pump is not filling. Criteria that have been suggested include load at a fixed position in the downstroke, maximum load, and area inside of the rectangle (often referred to as the surface card area).
The following are but a few of the many patents in this area of utilizing a surface card for control of a sucker rod pump.
For example, U.S. Pat. No. 3,951,209, issued Apr. 20, 1976 to Gibbs, describes a controller that measures at the surface both the load on the rod string and the displacement of the rod string. From these measurements, one can obtain a surface card and the area of the card will be the power input to the rod string. Since the pumping system will be lifting less fluid when the well pumps off, the power input to the rod string will also decrease. The decrease in power will result in a decrease in the area of the surface dynamometer card. This decrease in area is used as an indication of a pump-off condition and the pumping unit is shut down.
U.S. Pat. Nos. 5,006,044, 5,362,206 and 5,372,482 disclose methods to monitor electric motor power consumption as an indicator of work being performed by the sucker rod pump.
U.S. Pat. Nos. 5,224,834, 5,237,863, 5,252,031, and 5,314,016 disclose various method to monitor and control sucker rod pumps using a strain gauge either located on the polish rod or on the beam of a beam pumping unit as an indicator of load. A common shortcoming of the beam-mounted strain gauges is the inability of the strain gauges to differentiate between strain caused by load on the beam or metal and strain caused by changing temperature of the metal. This problem is particularly noticeable when the strain gauge is mounted on the beam rather than the polish rod. The beam is otherwise a convenient place to mount the strain gauge for reasons that include less movement of the conduits to the gauge, and less need to remove the gauge when maintenance is performed on the pumping unit. The apparent load of the plot of load vs. position will therefore change due to variables such as temperature.
U.S. Pat. Nos. 4,583,915 and 5,423,224 suggest apparatus and methods to temperature compensate strain gauge measurements for changes in temperature. Both of these patents suggest methods that essentially zero-out changes in a measured parameter over a long time period so that slow drifts will be compensated out of the strain gauge output, whereas major changes will not immediately be compensated out, thus permitting the monitoring and control system to function without significant drift due to temperature changes. Because these systems eventually zero out all changes, the absolute level of load is never known, and even the load relative to a datum is not known. Further, these methods generally select one load measurement to hold constant. The maximum load, minimum load, and average load have all been used, and each has disadvantages. Generally, the maximum load will vary at the start of a pump off cycle, but be more consistent near the end of the cycle. The end of the pump off cycle is when it is most important to have reliable information to know if criteria for shutting down the pump is reached, but it would also be desirable to have accurate load compensation at the beginning of the pump cycle.
U.S. Pat. No. 3,306,210 discloses a pump-off controller that monitors the load on the polished rod at a set position in the downstroke. Pump-off is detected when the load exceeds a preset level at that set position. U.S. Pat. No. 4,583,915 discloses a pump-off controller that monitors an area outside the surface dynamometer card. More particularly, the patent discloses monitoring an area between the minimum load line and the load line at the top of the stroke. Other pump-off controllers have monitored the electrical current drawn by the drive motor to detect pump-off.
U.S. Pat. No. 4,490,094 discloses a pump-off controller that monitors the instantaneous speed of revolution of the drive motor during a complete or portion of the cycle of the pumping unit. Pump off is sensed by calculating a motor power from measured speed which is less than the motor power corresponding to a completely filled pump barrel. Both the surface load and position of the rod string can also be determined from the monitored instantaneous speed of the drive motor.
A major disadvantage of all of these “surface card” methods, is that the surface card is not always an accurate representation of the downhole rod string displacement (or position) and the downhole load on the rod string. Use of the surface card introduces errors caused by ambiguities in the surface card, the obscuring effects of downhole friction along the rods, as well as numerous other factors.
A more accurate representation, would be to utilize a “downhole card,” that is, a plot (as both are measured downhole) of load vs. rod string displacement (or position). As these measurements are not possible to easily obtain, methods exist to estimate this downhole card.
For example, U.S. Pat. No. 5,252,031 utilizes the surface determination of load and displacement of the rod string (by monitoring the position of the crank arm that reciprocates the walking beam) to calculate the downhole card.
As another example, U.S. Pat. No. 5,406,482, discloses the use of an accelerometer in the calculation of the downhole pump card.
The downhole pump card can also be obtained using other methods including the method described in U.S. Pat. No. 3,343,409, which utilizes surface measurements of load and position of the rod string to construct a downhole pump card. The downhole card is obtained by the use of a computer to solve a mathematical expression described in the patent.
Of course, an alternative is to construct an analog circuit of the pumping system. It will be appreciated that while an analog circuit provides an instantaneous downhole card, it is unique to the particular pumping system, and would have to be extremely sophisticated to account for any changes in the system.
However, in spite of the above advancements, there still exists a need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well.
There is another need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well, which do not suffer from the disadvantages of the prior art apparatus and methods.
There is even another need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well, which provide for near real time generation of a downhole card.
There is still another need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well, which allow for the concurrent viewing of the surface card and the downhole card.
There is yet another need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well, which provide graphical representation of the surface card and the downhole card in which the viewable graphical representation, the axis on the surface card representing position is at the same scale as the axis on the downhole card representing position.
There is even still another need in the art for apparatus, methods, and products for monitoring and/or operating a reciprocating well, which utilize surface card data and/or downhole card data in the operation of the well.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.